Thank you for PDF document. Your PDF document contains rectangle annotation without PDF annotation appearance, such document could be generated only if you disabled generation of PDF annotation appearance. Unfortunately, we cannot reproduce the issue using your code. Please send us (to support@vintasoft.com) a small working project which demonstrates the issue.

You also need add reference to Vintasoft.Annotation.Pdf.dll, this assembly allows to generate PDF annotation appearance and the assembly is necessary if you want to view saved annotations in Adobe PDF Reader.